Can you substitue cream of tartar with something else?

I'm going to bake this cake: a href="http://www.foodnetwork.com/recipes/food-network-kitchens/lemon-cake-with-lemon-meringue-frosting-recipe/index.html" rel="nofollow"http://www.foodnetwork.com/recipes/food-…/a It says to use cream of tartar but I don't have any of it, can I substitute it with something else?